A number of etiologic hypotheses have been, explored for a variety of cancer sites and exposures. Many of the studies have involved biochemical assessments to better define exposure. A major emphasis has been placed on defining the epidemiology of female tumors. particularly breast and cervical cancers. Breast cancer case-control studies have been undertaken in young women and in Asian-Americans. and most recently attempts have been made to understand regional differences in incidence. including excesses in the northeastern U.S. A large follow-up study of screening participants has examined breast cancer risk as well as all cause mortality in relation to exogenous hormone use. Mammographic predictors of subsequent breast cancer risk have also been defined. The role of the human papillomaviruses in the natural history of cervical neoplasia is being assessed in two large prospective studies. one in the U.S. and the other in Costa Rica. A study of cervical adenocarcinoma is being launched. Cohort studies are also underway to assess disease risk among twins as well as patients with cosmetic breast implants. prenatal exposure to diethylstilbestrol.different types of gynecologic operations. and various immunologic conditions. A multidisciplinary study of nasopharyngeal cancer in Taiwan is nearing completion. Further, a multi- center study has addressed the relationship of water contaminants to cancer risk. Also of interest is the relationship of cancer risk to occupational exposures. pursued through both death certificate studies (female breast) as well as prospective investigations (aerial pesticide applicators. radio amateurs). Descriptive analyses have been pursued for certain cancer cites (cervix. ovary. melanoma. second tumors following rare reproductive cancers) as well as for selected exposures (hair dyes).